Self-Injury in Autism May Be Sign of Pain

Study findings contradict traditional explanation

Action Points

Note that this study was published as an abstract and presented at a conference. These data and conclusions should be considered to be preliminary until published in a peer-reviewed journal.

BALTIMORE -- People with autism who engage in severe self-injurious behaviors may be experiencing heightened sensations to pain and acting out accordingly, researchers said here, contradicting a commonly held belief that such individuals are insensitive to pain.

Patients with lower functioning autism are most likely to engage in self-injurious behavior, said lead study author James W. Bodfish, PhD, of Vanderbilt University School of Medicine in Nashville, Tenn., based on two studies comprising 447 adults and children with intellectual or developmental disabilities. These individuals may have an altered nociceptive function so they perceive pain even from nonpainful stimuli, and may exhibit biological changes in skin nerve fibers or chemicals like cortisol related to pain and stress, Bodfish said.

Bodfish and colleagues conducted two studies to try to define which individuals with autism engage in self-injurious behavior. In the first, they enrolled 81 children with autism ages 8 to 16. Of these, 41 had high-functioning autism and an IQ greater than 90, while 30 were defined as low-functioning with autism plus intellectual/developmental disabilities and an IQ less than 70. Investigators asked parents whether their children engaged in self-injurious behavior and did their own observations, finding serious self-injurious behavior only in the lower functioning group.

Parents reported that 63% of the low-functioning group engaged in self-injurious behaviors versus 24% of the high-functioning group; moreover, the investigators noticed those in the high-functioning group were more likely to engage in milder behaviors like skin picking or scratching. Redefining injuriousness to include more serious behaviors led to categorization of 56% of the low-functioning group as engaging in them versus 0% of the high-functioning group.

Anxiety was associated with milder self-injurious behavior in the high-functioning group, while repetitive behaviors were associated with the more serious self-injurious behavior in the low-functioning group.

Because those with lower functioning autism don't necessarily have the verbal skills to express pain, the investigators conducted a second study to try to measure sensory sensitivity objectively. They enrolled 366 adults with intellectual/developmental disabilities ages 20 to 55. All were minimally verbal with an IQ less than 50. Of this group, 34 had autism, intellectual/developmental disabilities and self-injurious behavior; 17 had intellectual/developmental disabilities only with no history of self-injurious behavior. Those in the first group engaged in self-injurious behavior hourly if not daily, and had been in treatment for the behaviors for at least 5 years.

In a modified quantitative sensory testing procedure, investigators tested five types of stimuli -- a pin prick, warm touch, cool touch, deep pressure, and light touch -- as well as some sham stimuli by applying them to the backs of participants in five-second intervals, while a video camera in front of them recorded their facial expressions. Researchers blinded to other information about participants used the facial action coding system (FACS) to identify signs of pain based on changes in facial action units (FAUs) expressed by the participants, such as closing the eyes or raising the cheeks.

Researchers saw more facial action response to active stimuli versus sham stimuli, and those in the self-injurious behavior group had significantly higher FAU response than those in the control group.

Investigators also set out to study validated biomarkers of pain used outside of autism. They took a 3-mm skin biopsy from the backs of study participants (an area generally not damaged by self-injurious behavior) to examine the density of epidermal nerve fibers and measure changes in immunohistology. They also took saliva samples from the participants to measure biomarkers of stress/pain like cortisol, substance P and α-amylase.

Among samples from the self-injurious behavior group, researchers observed significant gaps between bundles of nerve fibers, and tufting of nerve fibers, that were not seen in the control group. These correlated to the FAU results (r=0.47, P<0.001). They also noticed mast cell degranulation, a marker of inflammatory response in pain conditions, among skin samples from the self-injurious behavior group. Finally, the researchers found increased levels of cortisol, α-amylase and substance P in saliva samples from those in the self-injurious behavior group.

"Our work suggests that at least a subgroup of individuals with severe and persistent self-injury may be in a physiological state similar to neuropathic pain or hyperalgesia associated alterations in inflammatory, immune, and nociceptive systems," Bodfish said. "If so, this may provide a set of accessible, objective biomarkers of altered sensory function that may help identify the need for treatment and perhaps also mark the course of treatment response in this vulnerable but under-researched subgroup."

While the results would need to be replicated, "the toolbox for working with self-injurious behavior should include measuring pain," Bodfish said. "Together our behavioral and biologic methods have converged to suggest alterations in pain signaling in individuals with self-injurious behavior. What's intriguing to us is this could provide a new set of biologic targets that could be used in translational research."

The study was funded by the Eunice Kennedy Shriver National Institute of Child Health and Human Development, the National Institute of Mental Health, and The Mayday Fund. Bodfish disclosed no relevant relationships with industry.

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